The use of carbon-graphite fibers in a matrix for constructing a composite shaft for various pieces of sporting equipment is well known. Specifically, numerous shafts have been constructed of carbon-graphite reinforced composite material by wrapping lamination of plies of fibers impregnated with uncured epoxy onto a mandrel having the desired shape of the finished product and subsequently cured into that final shape. Normally a plurality of laminations are built up in this manner. Various proposals for location of the fibers relative to the longitudinal axis of the shaft have been proposed and have been manufactured.
As is well known, high modulus carbon-graphite fiber fabrication is much more expensive than standard modulus carbon-graphite and shafts made from carbon-graphite fiber for greater torsional stiffness of necessity are quite expensive.
The present invention provides a shaft having a plurality of circumferential sections which make up the shaft, with only a partial number of the sections comprising standard modulus carbon-graphite fibers in an epoxy resin matrix and the remaining outer portions comprising fiberglass fibers in a matrix. The circumferential sections comprise at least two inner plies of angle carbon-graphite at opposing angles, at least one zero ply of fiberglass, and at least one zero ply of standard modulus carbon-graphite. In order to provide the strength at the hosel for this type of shaft, which is the equivalent of the strength provided by typical regular hosel diameter standard modulus carbon-graphite reinforced composite golf shafts, the tip end of the shaft where it is connected to the hosel of the club head is of a substantially larger diameter than the standard golf club shaft. By using the specific method of the present invention of enlarging the tip outside diameter and laying the oriented standard modulus standard modulus carbon-graphite fibers with the proper proportion of lower-cost fiberglass reinforcement in the outer layers of the laminate, a very good performance shaft results which is suitable for a wide range of players.
The invention will be more clearly understood from the following description, taken together with the drawings.